1. Field of the Invention
The present invention is generally in the field of semiconductor devices. More specifically, the invention is in the field of semiconductor amplifiers,
2. Related Art
Power amplifiers, such as power amplifiers used in cellular handsets as well as other wireless communication devices, are typically designed and biased for optimum quiescent current in order to meet high output power specifications. However, the same quiescent current that is optimal for high power levels is not optimal at low power levels. By way of background, quiescent current refers to the current drawn by an amplifier when the amplifier is not receiving an input signal. Excessive quiescent current in power amplifiers at low output power levels causes an undesirable increase in power consumption, which can reduce battery life in portable communication devices, such as cellular handsets.
Conventional techniques to reduce quiescent current in power amplifiers at low output power levels have employed an external control pin, which can be either digital or analog. A digital control pin has a low mode and a high mode to switch from low to high quiescent current, while an analog control pin requires a continuous input voltage to control the amount of quiescent current supplied to the power amplifier for a specified power output.
However, during the switch from low to high quiescent current and vice versa, a digital control pin can introduce undesirable gain, phase, and power discontinuities in the power amplifier. Furthermore, a digital switch also requires baseband circuitry to switch the power amplifier from low mode to high mode when the power amplifier reaches saturation in low mode. On the other hand, conventional techniques that employ an analog control pin require more complex baseband circuitry and time-consuming testing and calibration procedures.
Thus, there is a need in the art for an effective means for reducing quiescent current at low power output levels in a power amplifier, such as a power amplifier used in a cellular handset.